1. The problem statement, all variables and given/known data Consider electrons of kinetic energy 5eV and 500keV. For each electron, what would be the particle speed, phase velocity, group velocity, and Broglie wavelength? 2. Relevant equations lambda = h/p (lambda = broglie wavelength) K.E. for nonrelativistic calcualtion = p^2/(2m) phase velocity = lambda*f = lambda / time group velocity = dw/dk 3. The attempt at a solution So for the 5eV case, I found that since the energy is low, i can use non-relativistic calculation. I find the Broglie wavelength to be around 0.548 nm and the momentum to be 1.208E-24 kg(m/s). Knowing the momentum, I used p=mv to find the particle velocity, which came out to be around 1.326E6 m/s. So far I think I am doing it right, but I cannot find the phase velocity nor the group velocity. Something tells me that for a non-relativistic case, the phase velocity is equal to c and the group velocity is equal to the particle speed. Can anyone explain this to me? Also, how should I approach the 50keV electron case, since the energy is so high I need to use relativity. Thanks.